JP3102795B2 - Heat-sensitive stencil film - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a heat-sensitive stencil film, and more particularly, to a heat-sensitive stencil capable of performing high-quality plate-making and printing without curling, high sensitivity, and no head dirt. The present invention relates to a film that can be formed by laminating a base paper with a porous support.

[Related Art] Heat-sensitive stencil printing usually uses a base paper in which a porous support having ink permeability and a hot-melt perforated film are bonded directly or via an adhesive, and a desired character is printed on the base paper film. A plate is made by heat-perforating figures, shapes, and other shapes, and printing is performed using this plate. The method of making this plate is digital plate making using a thermal head (hereinafter abbreviated as TH method), infrared radiation, xenon, and the like. A method of irradiating a flash light (hereinafter, abbreviated as a flash method) is already known. In particular, the TH method has advantages such as low printing cost when printing a large number of sheets and high-speed printing as compared with electrostatic copying (PPC), and is rapidly spreading to offices and schools. .

On the other hand, as a method for laminating a hot-melt perforated film and an ink-permeable porous support, a normal laminating method such as a dry laminating method and a wet laminating method, and the method described in Japanese Patent Publication No. 55-47997. It is known to use a conventional laminating method or the like.

The base paper manufactured in this manner easily curls inward on the film side due to laminating conditions or changes in temperature and humidity during storage. When the curl becomes large, handling and transportability of the stencil in the stencil printing machine become poor, causing troubles such as clogging of the stencil. Especially recently,
For the purpose of high-speed plate making, low-energy plate making, and high resolution, a film with improved perforation sensitivity, for example, a film with improved shrinkage at 150 ° C. to improve perforation (JP-A-63-312192) In this case, although the perforation sensitivity is improved, the conventional laminating method has a disadvantage that the curl of the base paper is large due to a large amount of shrinkage during lamination.

As a method of reducing the curl of the base paper, for example, a method of applying tension to an ink-permeable porous support, extending the film, laminating the film on a film, and laminating the film (Japanese Patent Application Laid-Open No. 1-156096).
Has been proposed. According to this method, the curl immediately after the production of the base paper is good, but the curl occurs when there is a large change in temperature and humidity during storage. In particular, recently the film thickness has been extremely thin, 1 to 3 μm to reduce perforation energy, and the control of the tension when laminating this film is very delicate, and it is adopted as a continuous mass production technology for base paper. Difficult to do.

In addition, in the TH method, since a film is instantaneously melt-punched with a high-temperature thermal head, there is a problem that a stick phenomenon occurs between the thermal head and the film. In this case, even if thermal fusion occurs even in a small portion of the heating element of the head, unlike the flash method, the head (heating section) and the film are constantly moving relative to each other. Problems occur.

As a method for preventing this, it has been proposed to form a release layer by applying a surfactant or a silicone oil layer on the film surface (for example, JP-A-60-19592, JP-A-60-97891). issue).

The formation of the release layer is effective in preventing thermal fusion to the head, but if the adhesion between the film and the release layer is not sufficient, the release layer will peel off and adhere to the head in a scum. In this case, although the stick phenomenon does not occur, when plate making is performed a number of times, the amount of deposition on the head increases, heat transfer to the film is reduced, so that the perforation is reduced, the print density is reduced, or the image clarity is reduced. Occurs.

[Purpose] It is an object of the present invention to provide a heat-sensitive stencil film having excellent perforation sensitivity, small curl even under various temperature and humidity conditions, and little heat-sensitive head dirt even in multiple plate making. is there.

[Constitution] The object of the present invention is to provide a biaxially stretched film of aromatic polyester having a thickness of 0.5 to 3.5 μm, wherein the shrinkage at 70 ° C. is 0.20% or less, and the shrinkage at 150 ° C. is 1.5% or more. And the in-plane refractive index of the film is
It is achieved by a film for heat-sensitive stencil paper characterized by being at least 1.485 and less than 1.500.

The biaxially stretched film made of an aromatic polyester needs to have a thickness of 0.5 to 3.5 μm, preferably 1.0 to 2.5 μm. If the thickness of the film is too thin, the perforation accuracy is reduced, and the film is unclear and tends to have shading. On the other hand, if the film is too thick, printing is lost or the thickness becomes uneven, which is not preferable.

The biaxially stretched film in the present invention needs to have a shrinkage at 150 ° C. of 1.5% or more, preferably 2% or more. If the shrinkage is small, the heat-sensitive piercing property of the film becomes poor, which is not preferable. On the other hand, if the shrinkage is too large, the base paper will curl with the fill side inside. Therefore the shrinkage at 150 ° C is 70
It is necessary to consider the balance with the shrinkage at the temperature of ° C, but it is preferable to keep it at 5% or less.

The feature of the biaxially stretched film in the present invention is that the shrinkage at 70 ° C is set to 0.20% or less, preferably 0.15% or less while the shrinkage at 150 ° C is maintained at 1.5% or more, preferably 2% or more. is there. This makes it possible to significantly reduce the occurrence of curl without deteriorating the heat-sensitive perforability of the film, and to a level that does not cause a practical problem.

The relationship between the shrinkage at 70 ° C. and the curl of the biaxially stretched film is considered as follows.

Base paper is usually produced by laminating a porous support such as porous thin paper, gauze or the like with a film via an adhesive, and further coating a release layer on the film. In the drying step, a heat treatment, usually a heat treatment at 60 to 80 ° C., is performed. Then, the shrinkage of the film under the processing conditions acts as a shrinkage stress on the film side of the base paper, causing curl. Therefore, it is effective to reduce the shrinkage at 70 ° C. of the film to prevent curling.

For example, in the case of polyethylene terephthalate film
The temperature of 70 ° C is a temperature near the polymer glass transition temperature, so that the shrinkage at 70 ° C depends on the residual stress inherent in the film. Therefore, when the film is stored for a long period of time, this shrinkage ratio tends to decrease.However, this requires a large storage space industrially. Need to be smaller.

The biaxially stretched film can be produced by a method known in the art, except that the film is subjected to the above-mentioned treatment for exhibiting the film characteristics. For example, the aromatic polyester is sufficiently dried at a predetermined temperature, supplied to an extruder, extruded in a molten state from a die onto a rotary cooling drum, and the molten film is closely adhered to the drum and quenched and solidified to form an unstretched film. Subsequently, a method of subjecting the unstretched film to biaxial stretching and heat setting to form a biaxially stretched film is usually used. Preferable examples of the biaxial stretching method include a sequential biaxial stretching method, and a multi-stage stretching method in which the film is sequentially stretched in the longitudinal direction after the successive biaxial stretching. The stretching ratio is usually 2.5 to 5 times in each of the vertical and horizontal directions. In addition, heat fixation is usually performed at a temperature of 100 to 250 ° C and a relaxation rate of 20%.
Performed below.

The adjustment of the shrinkage at 150 ° C of the biaxially stretched film
For example, as described in JP-A-63-31292, it can be carried out by adjusting heat treatment conditions after biaxial stretching. The contraction rate can be increased by relaxing the heat treatment conditions. For example, the contraction rate can be increased by decreasing the heat treatment temperature. However, when this temperature is lowered, the shrinkage at 70 ° C. necessarily increases.

70 ° C while maintaining the shrinkage at 150 ° C at 1.5% or more
As a method for reducing the shrinkage ratio in (1), it is particularly effective to adjust the tension at the time of winding the film or the pulling tension after leaving the heat treatment step after biaxial stretching.
By reducing these tensions, the shrinkage at 70 ° C. can be reduced.

In order to impart more curl reducing properties to the biaxially stretched film in the present invention, in addition to the above-mentioned shrinkage characteristics, in particular, the refractive index in the plane direction of the polyester film (hereinafter sometimes abbreviated as nz) is 1,485. More than 1,500,
Further, it is preferable to be 1,487 or more and less than 1,500.

The reason that the in-plane refractive index contributes to curl reduction is considered as follows.

The cause of the curl is considered to be a difference in the expansion of humidity between the porous support and the film, in addition to the above-mentioned heat shrinkage. For example, paper which is usually used as a porous support has a humidity expansion coefficient of 1 ×.
10 ^-4 ~7 × 10 is about ^-5% RH, whereas films such humidity expansion coefficient of the polyester film having a thickness of 2.5μm is 10 × 1
It is about 0 ^-6 RH, and it can be said that the stencil sheet to which both are bonded has an intrinsic factor of curling toward the film side under high humidity from the difference in the coefficient of humidity expansion. However, since the thickness of the paper is generally much larger than the thickness of the film, no curl is exhibited only by the difference in humidity expansion.
It is considered that when the shrinkage at the temperature of ° C. is large, curl is generated by a synergistic action.

The in-plane refractive index (nz) of the film becomes relatively large as the orientation of the biaxially stretched film in the longitudinal and transverse directions is reduced. It is understood that by reducing the vertical and horizontal orientations, the coefficient of humidity expansion increases, and as a result, the difference from the coefficient of humidity expansion of the paper decreases, and curling hardly occurs. However, if the in-plane refractive index (nz) is larger than 1,500,
It is not preferable because the mechanical strength of the film is reduced and becomes insufficient, and problems such as poor handling properties occur.

The in-plane refractive index (nz) of biaxially stretched film is 1,485 or more
When it is less than 1,500, it is effective for curl reduction, but at the same time, the advantage of improving the adhesiveness between the film and the release layer can be obtained. This improvement in the adhesiveness reduces the amount of scum deposited on the head, and does not cause a decrease in print density or bleeding even in a large number of plate making and printing, so that the same clear image as at the start of plate making and printing can be obtained.

The heat-sensitive stencil film of the present invention may be subjected to a corona discharge treatment in an air, carbon dioxide or nitrogen gas atmosphere on the surface of the film in order to improve the adhesiveness to the porous support. Further, another easy adhesion treatment may be performed. Further, this film may contain a courageous or inorganic additive to improve the slipperiness.

As a porous support for laminating the above-mentioned film,
Although not particularly limited, typical examples thereof include Japanese paper, songbook paper, synthetic fiber papermaking, various woven fabrics, and nonwoven fabrics. The weight of the porous support to be used is not particularly limited, but is usually ^{2 to 20} g / m ² , preferably 5 to 15 g / m ² .
g / m ² is used. When a mesh sheet is used, it is preferable to use a woven fiber having a thickness of 20 to 60 μm, and it is preferable to use one having a lattice spacing of 20 to 250 μm.

The adhesive used for bonding the film and the porous support of the present invention is not particularly limited, but examples thereof include vinyl acetate resins, acrylic resins, urethane resins, and polyester resins. Can be.

EXAMPLES Hereinafter, the present invention will be further described with reference to examples. The characteristics in the examples were measured by the following methods.

1) Shrinkage of the film The film is sampled in a 1 cm wide strip, marked with a certain distance (usually 10 cm), then kept in an oven heated to the following specified temperature for a specified time, and then room temperature Then, the distance between the marks was measured, and the shrinkage ratio was calculated from the following equation.

[However, l ₀ : distance between marks before heating and holding l: distance between marks after heating and holding] (a) Shrinkage rate at 150 ° C. The heating temperature was 150 ° C. and the heating and holding time was 30 minutes.

(A) Shrinkage at 70 ° C. The heat shrinkage was determined at a heating temperature of 70 ° C. and a heating holding time of 60 minutes.

2) Refractive index in the plane direction The refractive index in the plane direction of the film was measured using an Abbe refractometer manufactured by Atago Co., Ltd. and using a sodium lamp as a light source.

3) Plate-passing properties A plate-passing test of base paper was performed in a high humidity environment with a relative humidity of 70% or more, and the transportability was evaluated according to the following criteria.

Transportability evaluation criteria ◎: There is almost no curl, and printing is performed well. ：: There is some curling, but printing is performed. ×: Curling is large and the frequency of trouble in printing is high. △: Intermediate between ○ and × 4) Thermal sensitivity Head dirt Thermal stencil printing machine (Ricoh Co., Ltd .: Preport SS88)
In 0), the state of adhesion of the volume on the thermal head after plate-making for a 1000 plate using a general character document was evaluated visually or by a microscope or the like according to the following criteria.

Evaluation criteria for head dirt ○: Little head dirt △: Slight head dirt x: Severe head dirt and hardly see head background Examples 1 and 2 and Comparative Examples 1 and 2 Intrinsic viscosity (o-chlorophenol) , 35 ° C.) After sufficiently drying polyethylene terephthalate of 0.62, melt-extruding it into a sheet by an extruder, quenching and solidifying it by an electrostatic casting method to form an amorphous sheet, and then, moving the sheet vertically to 3.3 to
Stretched 3.6 times, 3.7-3.9 times in the horizontal direction, and 200-230 ° C
Heat treatment for about 1.5 seconds, and the physical properties shown in Table 1
A 2.0 μm biaxially stretched film was obtained.

 Then furum tetran For heat-sensitive stencil by laminating with gauze
Base paper was made. Table 1 shows the characteristics of the base paper.

As is clear from Table 1, according to the films of Examples 1 and 2, it is possible to obtain a heat-sensitive stencil sheet having little curl and no head dirt.

[Effects of the Invention] According to the film of the present invention, the occurrence of curl, which is a problem in handling high-sensitivity heat-sensitive stencil paper, is reduced or prevented, and head dirt is reduced even in plate making many times.
A heat-sensitive stencil sheet with excellent perforation sensitivity and image quality can be manufactured.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuyoshi Saito 3-37-19 Koyama, Sagamihara City, Kanagawa Prefecture Inside the Sagamihara Research Center, Teijin Limited (72) Inventor Hiroshi Tomita 3-37-19 Koyama, Sagamihara City, Kanagawa Prefecture Teijin Limited Sagamihara Research Center (72) Inventor Kotaro Kato 3-37-19 Koyama Sagamihara City, Kanagawa Prefecture Teijin Limited Sagamihara Research Center (56) References JP-A-63-160895 (JP, A) 62-282983 (JP, A) JP-A-2-307789 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41N 1/24 102

Claims (1)

(57) [Claims] 1. A thickness of 0.5 to 3.5 made of an aromatic polyester.
μm biaxially stretched film, the shrinkage at 70 ° C. is 0.20% or less, the shrinkage at 150 ° C. is 1.5% or more, and the in-plane refractive index of the film is 1.485 or more and 1.500
A film for heat-sensitive stencil base paper, wherein